Working and construction of Dropping mercury electrode

working and construction of dropping mercury electrode

The dropping mercury electrode (DME) is a type of electrode that is made of mercury is used in polarography. Experiments conducted using mercury electrodes are referred to be kinds of polarography. Even if the experiments are identical to or extremely close to a related voltammetry experiment that utilizes solid working electrodes. Working and construction of Dropping Mercury Electrode are given in detail here.

When examining reaction mechanisms related to redox chemistry and other chemical phenomena, these electrodes, like other working electrodes, are employed in electrochemical experiments employing three electrode systems.

Mercury is continuously fed into the polarisation solution through its capillary tubes from a reservoir (internal diameter of 0.3 mm to 0.05 mm).

It is discharged in small, homogeneous drops under polarisable micro-electrodes with a head of 40–60 em of mercury from a resistance-glass capillary (0.05–0.08 mm in diameter and 5–9 mm in length).

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Structure of Dropping mercury electrode

In this process, a flow of mercury crosses through an insulating capillary that produces a droplet. forming a droplet that consistently emerges at the capillary’s end. Each droplet expands until it is roughly a millimeter in diameter, at which point it releases.

Since the working electrode’s contact is above the capillary, the discharged droplet is no longer in contact with it. Mercury gathers in the cell’s bottom as the electrode is utilized. This mercury pool is sometimes employed as the cell’s auxiliary electrode by connecting it to a lead. Another drop immediately emerges in response to each discharged drop. The average frequency at which the drops are produced is 0.2 Hz.

Construction of Dropping mercury electrode

  • A Mercury reservoir vessel
  • A Capillary
  • Standing tube with a stopcock nearby. 5.5 centimeters of Corning marine barometer tube and 6 millimeters of soft glass are combined to form the capillary tube.

Advantages of Dropping mercury electrode

  • Each drop of the DME has a smooth, clean surface free of any impurities or adsorbed analytes, which is a significant benefit.
  • Its surface is continuously renewed, making it smooth, replicable, and free from the danger of passivity or toxicity.
  • Unlike a solid electrode, the self-renewing electrode does not require cleaning or polishing.
  • This benefit is at the expense of a functioning electrode with a variable surface area.
  • The diffusion current attains a stable value after a change in the applied voltage that is repeatable.
  • The fluctuating surface area can be accounted for or even utilized to your advantage because the droplets are produced predictably.
  • As the drops grow, the capacitive current is added to the faradaic current more and more.
  • Mercury has a strongly electronegative hydrogen overpotential, which allows for the deposition of difficult-to-reduce materials including manganese (II) ions, aluminum ions, and alkali metallic ions. Current-potential curves for these ions cannot be obtained with a platinum microelectrode.
  • We can get the surface area from the drop weights.
  • In trials where the potential is continuously adjusted, these shifting current effects can lead to noisy traces.

When mercury is subjected to a potential difference of at least +0.4 volts, it dissolves and releases mercury ions, which also produce an anodic wave. Placing the electrode on a surface with a potential difference between +0.4 and -2.0 volts causes mercury ion oxidation.

Working of Dropping mercury electrode

The counter electrode is designed to use mercury as either the cathode or anode, with DME acting as the anode. A counter electrode cannot be polarized. An electrolyte solution, such as KCl, is combined with the analyte solution to produce concentrations that are 50–100 times greater than those of the sample. Oxygen will be expelled (removed) from the solution by bubbling pure nitrogen or hydrogen gas through it. The polarographic cell is given a voltage, and the current is then measured. An inverse voltage-versus-current graph is produced. Polarograph is the graph and Polarogram is the tool as a consequence.

Hanging mercury drop electrode

A working electrode variant of the dropping mercury electrode is the hanging mercury drop electrode (HMDE) (DME). Polarographic experiments are those that use mercury electrodes that drop. Voltammetry is the term used when tests are carried out at an electrode with a fixed surface, such as the HMDE.

When researching reaction mechanisms related to redox chemistry and other chemical phenomena employing three electrode systems, these electrodes are used similarly to other working electrodes in electrochemical investigations.

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Difference between Dropping mercury electrode and Hanging mercury electrode

  1. A partial mercury drop with regulated geometry and surface area is produced by the hanging mercury drop electrode at the capillary’s end, as opposed to the dropping mercury drop electrode, which continuously releases mercury droplets during an experiment.
  2. The  Hanging mercury electrode does not suffer from the drawbacks a Dropping mercury electrode has from a surface that is continually changing because it has a static surface area during an experiment.
  3. The self-renewing Hanging mercury electrode may simply release the contaminated drop and grow a clean drop between each experiment, unlike solid electrodes that often require cleaning and polishing.


What is the principle of dropping mercury electrode?

The basic idea involved weighing mercury drops as they fell into a solution through a glass capillary with a thick wall. The layer of mercury accumulating at the bottom of the vessel acted as the second electrode, while the mercury that was falling from the sky and coupled to a source of d.c. voltage served as the first electrode.

Why dropping mercury electrode is used in polarography?

The dropping mercury electrode (DME) is a silver electrode used in polarography. Mercury is continuously fed into the polarisation solution through its capillary tubes from a reservoir (internal diameter 0.3 mm to 0.05 mm).

What is mercury dropping?

I acknowledge that using the phrase “as mercury drops” to indicate how chilly it is becoming is a novel idea. No. “When the temperature drops, ice develops on the water’s surface.” As the thermometer’s mercury drops, ice forms on the water’s surface.

Application of dropping mercury electrode

The mercury working electrode known as the dropping mercury electrode (DME) is utilised in polarography. Even if the experiments are identical to or extremely close to a related voltammetry experiment that utilises solid working electrodes, experiments conducted using mercury electrodes are referred to be kinds of polarography.

Disadvantages of dropping mercury electrode

Dropping mercury electrodes has the drawback that handling it should be done with caution due to its hazardous nature. A mercury drop’s surface area is never constant. Surface tension changes as a result of applied voltage, which also affects drop size.

Darshan Singh

The author has 20 years of experience in the Pharmaceutical Manufacturing Companies. Have exposure to all audit documents for WHO-GMP, PIC/S, USFDA, Export documents, US-FDA documents, Validation of Pharma machinery, and Quality Control Instruments. Expert in Pharma Plant Setup and sale and acquisition of running pharma company.
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